The present disclosure generally relates to an air-fuel ratio control system for internal combustion engines, and more particularly relates to an air-fuel ratio sensor early activation feedback system and method.
Exhaust gas sensors are often disposed in the exhaust passages of internal combustion engines for detecting an exhaust gas component concentration for the purpose of controlling the operation of the internal combustion engine or monitoring the status of an exhaust gas purifying system. Specifically, an exhaust gas sensor (e.g., a linear air-fuel ratio sensor) can be disposed at a certain location in the exhaust gas passage and has an element sensitive to an exhaust gas component state to be detected, the element being position for contact with the exhaust gas flowing through the exhaust passage. For example, an air-ratio sensor, such as an oxygen concentration sensor or the like, can be disposed as an exhaust gas sensor upstream or downstream of an exhaust gas purifying catalyst disposed in the exhaust passage for the purpose of controlling the air-ratio of the internal combustion engine to maintain the purifying ability of the catalyst. This is done by using the measured air-fuel ratio to adjust the amount of fuel injected into the engine.
Some air-fuel ratio sensors have a built-in heater for heating the active element thereof for increasing the temperature of the element and activating the element to enable the element to perform its essential functions and also removing foreign matter deposited on the element. For example, when the air-fuel ratio sensor is an oxygen concentration sensor or the like, it can have an electric heater for heating the active element thereof. One such exemplary sensor is a hot wire type that needs to be heated before proper operation is possible. After the internal combustion engine has started to operate, the electric heater is energized to increase the temperature of the active element of the oxygen concentration sensor to activate the active element and keep the active element active.
With recent stricter regulation of exhaust gases, there is an increasing demand for starting the feedback control of the air-fuel ratio as early as possible after the start of the engine, and hence it is desired that the oxygen concentration sensor should become activated as early as possible after the start of the engine. Conventionally, to promote activation of the sensor, as discussed above, the sensor is heated by a heater and this heating does not begin until after the engine is started. Of course, the sensor typically cannot be heated to the activation temperature instantly after the start of the engine and heating. Thus, immediately after the start of the engine, the oxygen concentration sensor is not fully activated, and therefore, until the sensor becomes fully activated, exhaust gases from the engine can contain considerable amounts of unburned HC and sulfur components and hence are in an unstable or unpurified condition.